1. Field of the Invention
The present invention relates to a digital broadcasting receiving apparatus and a scramble channel deciding method, and particularly to a digital broadcasting receiving apparatus, and a scramble channel deciding method capable of shortening time required for scramble decision for each channel in a case where a channel map is created in the digital broadcast receiving apparatus.
2. Description of the Background Art
In recent years, standardization and practical applications of digital broadcast have been advanced even in the field of television broadcast, and various techniques for transmission and reception of program data have been disclosed.
For example, Document 1 (Japanese Patent Laying-Open No. 2002-374472) discloses a technique in which in a digital broadcast receiving apparatus, in order to prevent PCR (Program Clock Reference) information of TS (transport stream) packets from becoming improper due to delay time occurring when a transport stream of a plurality of received programs is outputted externally, a PCR corrector corrects PCR data (Program Clock Reference value) with a value of STC (System Time Clock) counting means when the TS packets are externally outputted if the delay time occurs during the external output of the TS packets including PCR.
Moreover, Document 2 (Japanese Patent Laying-Open No. 09-130764) discloses a technique in which in order to shorten time required for changing a program number involving switchover of a physical channel, on the transmission side, a portion of a program number is set as a number of the physical channel, and a relation between the program number and a PID (packet identification) pointing to a PMT (Program Map Table) is fixed, while on the receiving side, a program association table is stored in advance. In such a technique, on the receiving side, the number of the physical channel is identified from the set program number when the program number is changed, and whether or not the number of the identified physical channel is the same as a number of a physical channel being received is decided. If the number is not the same, the channel is changed to the identified physical channel, and concurrently, in the PAT (Program Association Table) stored in the receiving apparatus, an elementary PID and a PCR_PID corresponding to the program number are extracted from a PMT having a PMT_PID (PID pointing to a PMT) corresponding to the program number, and a packet having the extracted elementary PID and PCR_PID is taken out from a transport stream to perform the program switchover.
Moreover, Document 3 (Japanese Patent Laying-Open No. 2001-346109) discloses a technique in which in a digital broadcast receiver, a PID of video data or audio data is predicted based on the channel number subjected to channel selecting instruction to achieve high-speed channel selection processing.
Furthermore, Document 4 (Japanese Patent Laying-Open No. 2001-333339) discloses a technique in which in a digital broadcast receiver, change in contents of an information table (PMT) is checked by checking a value of a CRC (Cyclic Redundancy Check), each PID of video, audio and PCR, and the like on a second-to-second base, and if there is any change, it is determined that the switchover of a program has been detected to set a program parameter described in the information table as a signal extracting parameter and to execute the channel change with the signal extracting parameter validated.
For the digital broadcast, a communication system by a conditional access system with payment of charge and the like as conditions is also realized. In such a communication system, whether or not descramble processing is required for each channel is decided.
At the time of the above-described requirement decision, in a system employing, for example, an MPEG-TS (Moving Picture Experts Group Transport Stream), in principle, the requirement decision has been performed based on a value of data in a bit field of “transport scrambling control” of a header of each TS packet, or in a bit field of “PES scrambling control” of a PES (Packetized Elementary Stream) packet. Based on the decision result, scramble information for each channel is stored on the receiving apparatus side as a table of a channel map, as shown in FIG. 6, for example.
In the table shown in FIG. 6, a plurality of sub-channels (sub Ch) (in some cases, one sub-channel) are defined in each physical channel (physical Ch). In each of the sub-channels, the scramble information (requirement for descramble processing) based on a TS packet is indicated in a field of “transport” and the scramble information based on a PES packet is indicated in a field of “PES”. In FIG. 6, if the descramble processing is required, or if the decision is disabled, “Y” is indicated, and if the descramble processing is not required, “-” is indicated. In FIG. 6, hatching is applied to the field corresponding to the sub Ch requiring the descramble processing. In the digital broadcast receiving apparatus, when an operation for switching outputted channels sequentially is performed, the channels requiring the descramble processing are skipped to switch the channel, as shown by arrow in FIG. 6.
Moreover, for the above-described communication system by the conditional access system, various techniques have been disclosed. For example, Document 5 (Japanese Patent Laying-Open No. 2002-271322) discloses a technique in which with each channel of digital broadcast, on the transmission side, PID information specific to a system indicating a PID as a scramble object is stored in advance, and is compared with PID information of each data packet to execute the scramble processing for the data packet, and on the receiving side, PID information specific to the system indicating a PID as a descramble object is stored in advance, and is compared with a PID of each received data packet to thereby select a packet as the object of the descramble processing.
In actual broadcast, the above-described bit field may not be provided in each received or transmitted packet. In this case, the decision of the requirement for the descramble processing based on the value of the specific bit field in the TS packet or the PES packet as described with reference to FIG. 6 is disabled.
In the above-described case, in creating a channel map, for example, for each sub Ch of each physical channel shown in FIG. 7, PIDs of video data (Video_PID) and/or PIDs of audio data (Audio_PID) configuring the sub Ch of interest are acquired based on a PMT 901 of the sub Ch of interest, as shown in a field 902 in FIG. 7. Based on the acquired PIDs, all packets of the video data and the audio data configuring the sub Ch of interest are acquired, and for each of the packets, whether or not it can be decoded properly by a decoder is decided, so that whether or not the sub Ch requires the descramble processing is decided based on the above-described decision result.
However, in this case, since whether or not the decoding is enabled is decided for each of the packets of the object channel, there has been a problem that the creation of the channel map takes long time, so that the operability at the time of channel selection in the receiving apparatus is deteriorated.
In the technique disclosed in Document 5, since the PIDs of the packets as the scramble/descramble objects need to be stored in advance in the transmitting apparatus and the receiving apparatus, there has been a problem that the configuration of the broadcast system is complex.